Sedimentary nitrogen dynamics in a coastal reef area with relatively high nitrogen concentration

The migration and transformation of nitrogen(N)in sediments play an important role in regulating the N concentration and nutrient structures in shallow seas.However,studies of sedimentary N dynamics are rarely focused on carbonate sediments,although these account for about 40%of the continental shelf area.Thus,the regulation mechanisms of the N dynamics in the carbonate sands of coral reefs are not clear.Taking the coral reef area of Weizhou Island,which has a relatively high N concentration,as the research object,we conducted a series of flow-through reactor experiments to investigate the fluxes of different N forms at the interface of sediment and seawater and their regulation mechanism by environmental factors.The fluxes of dissolved inorganic and organic N(DIN and DON)at different stations were-0.39-0.12 mmol/(m^(2)·h) and-0.18-0.39 mmol/(m^(2)·h),respectively.Denitrification(0.11-0.25 mmol/(m^(2)·h) was closely coupled to nitrification,which was limited by the availability of organic matter and its degradation product(i.e.,NH_(4)^(+)).Thus,the excessive NO_(3)^(-) might be reduced to NH4+by dissimilatory nitrate reduction to ammonium,rather than to N_(2) by denitrification.NO_(3)^(-) reduction peaked at intermediate advection rates(96 L/(m^(2)·h)) and flow path lengths(10 cm),but the release of DON also peaked at the same condition.In addition,climate warming would significantly affect sedimentary N dynamics at Weizhou Island.These results may help address the broader issue of the N cycle in coral reef eco systems under the dual pressure of climate warming and anthropogenic activities,and these results are beneficial to coral reef protection and local ecological management.

Responses of nutrient biogeochemistry and nitrogen cycle to seasonal upwelling in coastal waters of the eastern Hainan Island

The coastal upwelling has profound influence on the surrounding ecosystem by supplying the nutrient-replete water to the euphotic zone.Nutrient biogeochemistry was investigated in coastal waters of the eastern Hainan Island in summer 2015 and autumn 2016.From perspectives of nutrient dynamics and physical transport,the nutrient fluxes entered the upper 50 m water depth(between the mixed layer and the euphotic zone)arisen from the upwelling were estimated to be 2.5-5.4 mmol/(m^(2)·d),0.15-0.28 mmol/(m^(2)·d),and 2.2-7.2 mmol/(m^(2)·d)for dissolved inorganic nitrogen(DIN),phosphate(DIP),and dissolved silicate(DSi),respectively,which were around 6-to 12-fold those in the background area.The upwelled nutrients supported an additional plankton growth of(14.70±8.95)mg/m^(2)for chlorophyll a(Chl a).The distributions of nitrateδ^(15)N andδ^(18)O above the 300 m water depth(top of the North Pacific Intermediate Water)were different among the upwelling area,background area in summer,and the stations in autumn,and the difference of environmental and biogeochemical conditions between seasons should be the reason.The higher DIN/DIP concentration ratio,nitrate concentration anomaly,and lower nitrate isotope anomaly(Δ(15,18))in the upper ocean in summer than in autumn indicated the stronger nitrogen fixation and atmospheric deposition,and the following fixed nitrogen regeneration in summer.The higher values of Chl a and nitrateδ^(15)N andδ^(18)O within the euphotic zone in autumn than the background area in summer suggested the stronger nitrate assimilation in autumn.The differences in relatively strength of the assimilation,nitrogen fixation and atmospheric deposition,and the following remineralization and nitrification between the two seasons made the higherδ^(18)O:δ^(15)N and larger difference of enzymatic isotope fractionation factors^(15)εand^(18)εfor nitrate assimilation in summer than in autumn above the North Pacific Tropical Water.

Influence of TiB2 particles on machinability and machining parameter optimization of TiB2/Al MMCs

In situ formed TiB2 particle reinforced aluminum matrix composites （TiB2/Al MMCs） have some extraordinary properties which make them be a promising material for high performance aero-engine blade. Due to the influence of TiB2 particles, the machinability is still a problem which restricts the application of TiB2/Al MMCs. In order to meet the industrial requirements, the influence of TiB2 particles on the machinability of TiB2/Al MMCs was investigated experimentally. Moreover, the optimal machining conditions for this kind of MMCs were investigated in this study. The major conclusions are： （1） the machining force of TiB2/Al MMCs is bigger than that of non- reinforced alloy and mainly controlled by feed rate; （2） the residual stress of TiB2/AI MMCs is compressive while that of non-reinforced alloy is nearly neutral; （3） the surface roughness of TiB2/Al MMCs is smaller than that of non-reinforced alloy under the same cutting speed, but reverse result was observed when the feed rate increased; （4） a multi-objective optimization model for surface roughness and material removal rate （MRR） was established, and a set of optimal parameter combinations of the machining was obtained. The results show a great difference from SiC particle reinforced MMCs and provide a useful guide for a better control of machining process of this material.

Observation of viable alloskin vs xenoskin grafted onto subcutaneous tissue wounds after tangential excision in massive burns

Background:Staged excision and grafting with viable cryopreserved alloskin or fresh pigskin at an early stage is a main strategy for wound management in massive burns.Alloskin is the gold standard of a biological temporary skin substitute,and the main drawback to its wider use is the limited number of donors.In this paper,we compare the use of fresh pigskins to cryopreserved alloskins as temporary skin substitutes on subcutaneous tissue wounds after tangential excision by observing the clinical performances of these grafts in cases of a massive burn.Methods:We selected six adult massive burn patients undergoing tangential excision and skin grafting on subcutaneous tissue wounds(TESGSTW)at our burn center from January 1,2003 to December 31,2013.The general clinical data and survival percentage of skins at postoperative weeks(POWs)1,2,and 3 were analyzed.In our clinical practice,we also observed the phenomenon that several viable cryopreserved alloskin or fresh pigskin grafts used as temporary coverage on subcutaneous tissue wounds had long-term survival after repeated desquamation.The macroscopic and histological results of one typical case were also analyzed.Results:In this study,the first three TESGSTW operations were performed at 2–3,5–8,and 11–16 days post-injury.The operation areas were 30.3±7.9%total body surface area(TBSA),19.0±6.0%TBSA,and 12.0±1.7%TBSA,respectively.The survival percentage of the cryopreserved alloskins or fresh pigskins at POWs 1,2,and 3 were 80.0±10.0%vs 75.7±5.3%(t=1.01,P=0.16),71.2±10.6%vs 66.4±6.2%(t=1.09,P=0.30),and 48.7±2.5%vs 35.0±7.0%(t=3.83,P=0.03),respectively.The microscopic observation of the survival of alloskins or pigskins in one typical case showed rete ridges and a basilar membrane at the joint of the epidermis and dermis at an early stage;these structures disappeared with extended time post-operation.Conclusions:From the clinical observations,fresh pigskin and cryopreserved alloskins could be used with equal effectiveness at an early stage(within 2 weeks post-operation)as temporary coverage on massive burns after TESGSTW.After engraftment,several cryopreserved alloskins or fresh pigskins could co-survive in a massive burn patient for an extended amount of time.The co-survival of alloskin and pigskin will provide clues for further research into skin transplantation.